1. Field of the Invention
The invention relates to a processing head for a laser engraving or cutting apparatus and, more particularly, to an apparatus for processing stamp plates, provided with an enclosed housing in which the processing head and its lens support and gas blow nozzle are moveable in a controlled manner relative to a base for supporting a workpiece, the head being provided with a hood connected to a vacuum device for dust removal and terminating in spaced relationship from the surface of the workpiece.
Engraving rubber for text plates for use in stamps creates a lot of dust. Such dust, when swirling in the interor of a laser engraving apparatus, leads to soiling of lenses and mirrors and requires extensive cleaning operations. It also reduces the reliability as well as precision of the mechanical system.
2. The Prior Art
An apparatus of the kind referred to supra is already known from European Patent 0 330 565 B1. In it, nozzles are symmetrically and annularly arranged around a laser exit channel such that they blow gas inwardly in the direction of the focal point of the laser beam, for blowing away any dust. While this leads to swirling up of dust particles and their removal by the suction hood the severance force of the impinging gas jets is relatively low.
Good results as to the removal of dust created by laser engraving are obtained by a gas jet impinging obliquely on the focal point. However, the dust cannot be reliably removed because for reasons of safety the suction hood has to be placed at a certain distance from the surface of the workpiece; and a considerable quantity of the swirled-up dust will nevertheless escape to the surrounding process chamber of the enclosed housing, through the relatively narrow gap. Thus, an important aspect of the intended purpose is not satisfied.
It is an object of the invention to provide a processing head for a laser engraving apparatus which avoid this drawback and which substantially reduces the servicing requirements of the laser engraving apparatus.
In accordance with the invention, the object is accomplished by providing the processing head with at least two gas blow nozzles one of which is angularly disposed relative to the target of the vertically impinging laser beam while the other nozzle which is also angularly inclined relative to the laser beam, is directed toward a point of the workpiece surface laterally displaced from the point of impingement or target of the laser beam.
In this manner, it is possible by appropriately injected gas, such as air, an inert gas or another gas, to swirl up loose dust directly during an engraving operation and to remove it by the suction hood associated with the processing head or lens support so that it can in no circumstances escape to the surrounding processing chamber.
The basic concept of the invention is that while air blown in at an angle relative to the axis of the laser beam may be presented relatively easily, the velocity of the injected air is relatively low at the very point of impingement so that dust is removed in a very deficient manner. By contrast, in the embodiment in accordance with the invention, dust just created is swirled up and propelled away by an oblique gas jet aimed substantially in the direction of the focal point, and is retarded by the second jet aiming at a point intermediate the focal point and the outer margin of the suction hood. The retarding action of the second air jet prevents escape of the swirled-up dust from between the workpiece and the suction hood. Rather, it is suctioned off in a satisfactory and complete manner.